In known self-contained burglar alarms three switches are generally employed, namely a door switch which closes the alarm circuit upon opening of the door, a holding circuit switch which maintains the alarm signal device in energized condition despite reclosing of the door, and an on-off switch which in off position deactivates the alarm to open the door switch and holding switch circuits for deenergization of the alarm signal device. In such known alarm, should it be desired to operate the alarm so that the signal device is energized when the door is opened and is deenergized when the door is closed, then a fourth switch could be provided to open or bypass the holding circuit.